The invention relates to a radiation source according to the pre-characterizing clause of Claim 1 and to an arrangement for irradiation that incorporates such a radiation source.
Previous patent applications submitted by the present applicant, for example DE 197 36 462 A1, WO 99/42774 and P 10024731.8 (unpublished), have disclosed methods for treating surfaces, processing materials and manufacturing composite materials that involved the employment of electromagnetic radiation with a major effective component in the near-infrared region, in particular in the wavelength region between 0.8 μm and 1.5 μm. In several of these applications it is important for the irradiation to be incident upon a relatively wide area, to enhance the productivity of the method concerned. To achieve this goal, for the radiation source an elongated halogen lamp has been designed that comprises a glass tube with bases at the ends and at least one spiral filament, as well as an elongated reflector.
In known radiation sources or irradiation apparatus with elongated lamps having bases at both ends—for Instance, to be used for medical purposes or in illumination technology—the connectors or bases of such lamps are disposed coaxially at the ends of the glass tube; see, e.g., the patent documents U.S. Pat. No. 4,287,554 or DE 33 178 12 A1. These published documents also describe irradiation arrangements with several radiation sources disposed next to one another in parallel.
With a radiation source of this kind it is possible to irradiate a wide zone with a radiation flux density that is approximately constant over the entire width of the zone, which in turn makes the processing conditions uniform over a corresponding width of the material being processed. However, at the ends of the halogen lamp, in the vicinity of the bases, the radiation flux density decreases, so that in these regions other values of the process parameters apply. This is problematic in the case of applications that require a constant radiation flux density over the whole width of the product, because these regions are in principle not functional, so that the usable width of the irradiation zone, as far as processing technology is concerned, is smaller than the length of the radiation source.
Certain industrial processes that employ radiation in the near-infrared region (“NIR radiation”) can in principle be carried out with materials having very wide dimensions. However, to produce individual halogen lamps of a correspondingly large width is technically difficult and extremely expensive. To implement such processes it would be desirable to assemble several elongated halogen lamps having the standard dimensions in lengthwise alignment with one another, so that the total length of the assembly of lamps equals the length of the zone to be irradiated. However, the above-mentioned fact that the radiation flux density decreases near the bases of the glass tube of an individual halogen lamp proves to be a particularly severe problem in this regard. Hence the currently available radiation-source constructions cannot be employed for such applications if it is essential that the radiation flux density be constant over the entire width of the processing region.